496 



IdB 



bubble cavity 

 sheet cavity 



Uniform flow 



FIGURE 2. Development of noise and visual manifesta- 

 tion of cavitation at constant pressure vs. velocity, 

 in reference to the conditions of cavitation noise 

 detection. 



According to the location of cavitation zones: 



- vortex cavitation (in the cores of tip and 

 axial vortices) , 



- leading edge cavitation (on the suction side 

 and pressure side at the leading edge) , 



- blade-profile cavitation (in the region of 

 large blade thicknesses) . 



- root cavitation (at the blade roots) . 

 According to cavity pattern: 



- bubble cavitation (with cavities moving with 

 the flow through negative or increased pressure 

 zones) , 



- sheet cavitation (with cavities which on the 

 average are motionless in relation to the propeller) . 



By steadiness (uniformity) of the incoming flow: 



- steady cavitation (noise and other effects 

 result from the inner unsteadiness of the cavity 

 which is steady on the average) , 



- unsteady cavitation (noise and other effects 

 result from the cavity pulsations at an almost 

 regular frequency, the phenomenon of cavitation 

 buffeting) , 



- cavitation in an unsteady flow (noise and other 

 effects here again result from the pulsations as 

 well as from the probable disappearance of cavities 

 with the frequency of flow condition change) . 



It seems extremely difficult to provide a com- 

 parative description of noisiness for about three 

 dozen cavitation types characterized only by the 

 above-mentioned features. Some guidance is given 

 by the experimental data presented in Figures 2 to 

 5. 



In steady-state conditions the bubble cavitation 

 types are the most noisy (Figure 2) . Among cavita- 

 tion zones of different locations, vortex cavitation 

 types are the least noisy (Figure 3) , whereas 

 pressure-side, leading-edge cavitation types are 

 the most noisy (Figure 4) . 



In an unsteady (non-uniform) flow the relation 

 between the noisiness of sheet cavitation and that 

 of the bubble type is different (Figure 5) . 



The higher noisiness of the pressure-side leading- 

 edge cavitation is accounted for by the rapid 

 increase of pressure behind the suction zone (high 

 gradient) , which is typical of these conditions. In 

 case of the bubble structure of a cavity this rapid 

 pressure increase is accompanied by the increase 

 of acceleration during the collapse. In case of 

 the sheet structure it is accompanied by the 



IdB 



IdB 



- bubble cavity 



- sheet cavity 



Nonuniform flow 



FIGURE 3. Development of noise and visual manifesta- 

 tion of cavitation at constant pressure vs. velocity, 

 in reference to the conditions of cavitation noise 

 detection. 



- vortex cavitation 



- leading-edge 

 cavitation 



FIGURE 4. Development of noise and visual manifesta- 

 tion of vortex and leading-edge cavitation appearing 

 in succession in a uniform flow at constant pressure. 



